Case trim length

[J E Custom]

I'd be surprised if anyone here crimps or used a die with a crimp. Most use a bushing die. On gas guns and such people are more likely to crimp. As already stated just back the die off unless it won't bump the shoulder.

There are a few cases that can/should be crimped, but very few. Normally the largest cartridges and dangerous game cartridges are crimped, because of the benefit of being crimped, but you must use bullets with a cannelure. Bullets with cannelures are getting harder to find and fewer and fewer people are doing it.

Many large bore pistols for hunting also benefit from crimping. The main thing that has to be done before crimping Is trimming to less length than neck chamber to allow the case to open up correctly.

J E CUSTOM

 

[Scott E Ames]

There are a few cases that can/should be crimped, but very few. Normally the largest cartridges and dangerous game cartridges are crimped, because of the benefit of being crimped, but you must use bullets with a cannelure. Bullets with cannelures are getting harder to find and fewer and fewer people are doing it.

Many large bore pistols for hunting also benefit from crimping. The main thing that has to be done before crimping Is trimming to less length than neck chamber to allow the case to open up correctly.

J E CUSTOM

Like you I also use a crimp on all my 416 Rigby rounds and usually 3 or 4 338 Magnum rounds that are going to be placed in the magazine when shooting 250 and 275 grain bullets on a hunting trip.

 

[Shootin4fun]

After a lot of testing, I've seen little difference in cases that =/- .005 of each other in terms of MV ES/SDs. So total of .010" extreme spread. That tiny amount of extra or missing brass just doesn't seem to change the resistance to the bullet enough to make a difference. I anneal every or every other firing which made a tremendous difference. If I were shooting competition, I'd probably trim all to the same every time.

 

[Shootin4fun]

If I were crimping, I'd definitely trim every time, but I quit crimping rifle rounds decades ago.

 

[Philward]

Does every one trim back to minimum case length when trimming cases? Is there any advantage to only trimming too half way between Maximum and minimum case length?

Yes.
No.

 

[Philward]

I'm having trouble understanding how trim length affects powder capacity. Would you mind explaining that?

Maybe he was just being a smart*ss.

 

[Mram10us]

After the first firing, I resize then find the shortest and trim them all to that length. Neck doesn't allow extra powder capacity when we are talking .010"-.020".

 

[whirlwindjml]

Jesus I think i covid 19. My brain is not firing on all cylinders. Duh. Not even sure what I was thinking...

Shows how much we crimp round here.....

 

[fiftybmg]

The advantage to trimming to the long end of the spec is that you can get a wee bit more powder behind the bullet.

Trim length does not affect case capacity.

 

[greenejc]

Does every one trim back to minimum case length when trimming cases? Is there any advantage to only trimming too half way between Maximum and minimum case length?

The reason we trim cases to minimum length is to have a uniform length, which helps to give uniform grip on the bullet when loaded, and after annealing the case properly. Also, if you crimp your loads, which is required with some cartridges, the cases will be the proper length and you will get a uniform crimp. When I trim brass, I always trim back to minimum length.

 

[RD57]

If you use the Lee Factory Crimp Die and trim to minimum length you may not get any crimp. My 22 Hornet and 30-30 Lee FCD are guilty of this.

 

[greenejc]

If you use the Lee Factory Crimp Die and trim to minimum length you may not get any crimp. My 22 Hornet and 30-30 Lee FCD are guilty of this.

I haven't had that problem using the Lee Factory Crimp dies with Lee shell holders. I have had it on my .308 crimp die using RCBS shell holders, though. There seems to be a slight difference in thickness between the holders.

 

[fiftybmg]

The reason we trim cases to minimum length is to have a uniform length, which helps to give uniform grip on the bullet when loaded ...

That's a side effect of trimming, not why we trim.

The reason you must keep your cases to below specification length, is to prevent the case mouth being pinched in the throat when chambered.

Wether you trim to 0.001 or 0.003 below maximum is not too important.

If the case is too long, the case mouth is prevented from releasing the bullet normally, causing a pressure buildup. This can show as loosened primer pockets, blown out primers or a sticky / stuck bolt.

It may be that your rifle brass never needs trimming, but it should always be measured before each reload.

This applies to all bottleneck rifle brass, maybe someone can tell us if their 357 Magnum and larger straight wall rifle brass ever needed trimming.

 

[Tiny Tim]

I used to shoot IHMSA. M revolver class pistol was a Ruger Redhawk in 44 mag. Shot 2000-2500 rounds per year out of it. Don't remember how often I trimmed but it served two purposes. A uniform roll crimp, and it extends the life of the brass. It would thin around the case mouth and crack. This was 25 years ago, before we had all the annealing info we have today. Reloading straight walled pistol cases requires a heavy roll crimp with cast bullets and the flaring die combined with it works that case mouth ALOT!